Kept quiet and booked (9)
I believe the answer is:
preserved
'kept' is the definition.
(preserving is a kind of keeping)
'quiet and booked' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'and' is a charade indicator (letters next to each other).
'booked' becomes 'reserved' (similar in meaning).
'p'+'reserved'='PRESERVED'
(Other definitions for preserved that I've seen before include "Kept safe from harm" , "Prevented from decaying or spoiling" , "Prevented from decay" , "Maintained in an unaltered condition" , "Kept in an unaltered condition" .)